Lunate implant and method of stabilizing same

ABSTRACT

A lunate implant includes a one-piece, at least semi-rigid body defining a triquetrum face, a scaphoid face, a cupped, concave, distal surface adapted to articulate with the capitate bone, a proximal surface, a palmar surface and a dorsal surface. A pair of spaced, generally parallel suture passages extend between and open through the triquetrum and scaphoid faces. A pair of sutures are stitched to ligaments of the wrist. The ends of the sutures are passed through the suture passages so that one of the sutures has ends extending away from the triquetrum face and the other suture has ends extending away from the scaphoid face. The ends are grasped and the lunate implant is pulled down into the desired position in the distal carpal row of the wrist. The sutures are tied adjacent the implant to stabilize and position the implant.

BACKGROUND OF THE INVENTION

The present invention relates to arthroplastic reconstruction of thehuman joints and more particularly to implant resection arthroplasty ofthe wrist joint.

Surgical treatments of arthritis and similar conditions of the wristjoint have included intercarpal fusion, wrist fusion, local resection,proximal row carpectomy, bone grafting, radial styloidectomy, radialshortening or ulnar lengthening and soft tissue interpositionarthroplasty. Fusion procedures affect stability, power and mobility ofthe wrist. Local resection procedures, which involve removal of bone,are complicated by migration of adjacent carpal bones into the spaceleft by the resection which results in unwanted instability.

Various forms of flexible implants formed from silicone rubber have beendeveloped to replace the lunate bone of the carpal row. Such implantsare designed to act as articulating spacers capable of maintaining therelationship of adjacent carpal bones after excision of the lunate whilepreserving mobility of the wrist. An example of one such prior lunateimplant is found in U.S. Pat. No. 4,164,793, entitled LUNATE AND IMPLANTand issued on Aug. 21, 1979 to the present inventor. The implantdisclosed therein includes a one piece body of resilient materialdefining a planar triquetrum face. The face has a generally U-shape inplan and includes a stabilizing stem extending outwardly from andperpendicular thereto. The implant body, in addition, defines a scaphoidface, a cupped, concave, smooth distal surface, a proximal surface, adorsal surface and a palmar surface. The stem extending from thetriquetrum face is adapted to be inserted into an opening formed in thetriquetrum bone. The stem helps in stabilizing the bone and retaining itin the correct position.

In certain situations, it has been determined that a semi-rigid or arigid, metal implant is advisable. With a rigid material, a stabilizingstem cannot be inserted into an adjacent bone. The rigid stem could cutor damage adjacent bone structures. In certain situations, thestabilizing stem of the flexible implants has caused some erosion. Itwould be advantageous to avoid having to enter adjacent bone structures.Heretofore, proper stabilization of the implant has not always beenreadily achievable.

SUMMARY OF THE INVENTION

In accordance with the present invention, the aforementioned problemsare substantially eliminated. Essentially, a lunate implant fabricatedfrom a semi-rigid or rigid material such as a titanium alloy isprovided. The implant is configured to define a triquetrum face, ascaphoid face, a cupped, concave surface configured to articulate on thehead of the capitate, a proximal surface, a palmar surface and a dorsalsurface. The implant body further defines a plurality of suture passagesextending in spaced relationship between and through the triquetrum andscaphoid faces. The lunate implant is stabilized by suturing to twoadjacent ligaments of the wrist. A suture is stitched to a ligament andthe ends thereof are passed through the suture passages so that theyextend away from the triquetrum face. Another suture is stitched toanother adjacent ligament and the ends passed through the suturepassages so that they extend away from the scaphoid face. The ends ofthese sutures are grasped and the lunate implant may be pulled down intoposition. The sutures are then tied to define knots adjacent therespective scaphoid and triquetrum faces. The knot arrangement andsuture technique stabilizes the rigid implant. Problems heretoforeexperienced with stabilizing stems, bone cutting, erosion, instabilityand the like are eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, anterior view of the wrist joint showing thedistal and proximal carpal rows and the extrinsic ligaments of thewrist;

FIG. 2 is a fragmentary, posterior view showing the wrist and a portionof the hand;

FIG. 3 is a perspective view of the implant showing the scaphoid facethereof;

FIG. 4 is a perspective view of the implant in accordance with thepresent invention showing the triquetrum o medial face thereof;

FIG. 5 is an enlarged, fragmentary, plan view showing the method ofstabilizing the implant in accordance with the present invention;

FIG. 6 is a fragmentary, top plan view showing the implant sutured inposition in the wrist; and

FIGS. 7 and 8 show the positioning of the implant and method ofstabilizing the implant in the wrist.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, FIGS. 1 and 2 illustrate the human wristand extrinsic ligaments. As shown, the bones that make up the wristjoint include a proximal carpal row 12 adjacent the radius bone 14 andthe ulnar bone 16. The proximal carpal row includes a scaphoid bone 18,a lunate bone 20, a triquetrum bone 22 and a pisiform bone 24. Lunatebone 20 articulates proximally with the radius, distally with thecapitate and hamate bones, laterally with the scaphoid bone and mediallyabout the triquetrum bone. The proximal carpal row of the wrist and thedistal radius define the radial carpal joint. The wrist further includesa distal carpal row 28. The distal carpal row includes a trapezium bone30, a trapezoid bone 32, a capitate bone 34 and a hamate bone 36. Amidcarpal joint 38 of the wrist extends between the distal and proximalcarpal rows.

As illustrated in FIG. 1, the carpal bones are held together by shortinterosseous ligaments. The ligaments define a symmetrical pattern dueto insertions into the scaphoid, lunate, triquetrum and capitate bones.The ligaments include the radial collateral ligament (RCL) 42, theradioscaphocapitate ligament (RSC) 44, the radiolunate ligament (RL) 46,the radioscapholunate ligament (RSL) 48, the ulnolunate ligament (UL)50, the ulnocarpal meniscus homologue (M) 52, the lunotriquetralligament (LT) 54 and the deltoid ligament (V) 56. The ulnar collateraland radial collateral ligaments provide lateral support of the wrist. Inaddition, palmar radial carpal and dorsal radial carpal ligamentsmaintain support of the carpal area. The fibers of the palmar radialcarpal ligament extend distally and obliquely from the radius, thetriangular fibro-cartilage and styloid process of the ulna.

In accordance with the present invention, the lunate bone is replacedwith a lunate implant 60 (FIG. 2). Implant 60 is a one-piece body whichincludes a posterior or dorsal surface 62, a triquetrum face or medialsurface 64, a scaphoid face or lateral surface 66, a proximal surface68, a distal surface 70 and an anterior or palmar surface 72 (FIGS. 3and 4). Surfaces 66, 64 are planar and define an included angle "a"(FIG. 6). Angle "a" opens from the distal surface 70 to the proximalsurface 68. Surfaces 64, 66 are adapted to abut against and articulatewith the triquetrum and the scaphoid bones, respectively. These surfacesare generally U-shaped in plan. Distal surface 70 of implant 60 isconcave and smoothly cupped in shape. Surface 70 defines a capitatearticulating surface adapted to engage the head of the capitate bone 34.

The configurations of the surfaces of implant 60 are as disclosed in theaforementioned U.S. Pat. No. 4,164,793. Implant 60, however, does nothave a stabilizing stem. In addition, implant 60 is formed with a pairof spaced, generally parallel suture passages 76, 78. The suture passageextend immediately adjacent the edges of the peripheries of faces 64, 66and adjacent the surfaces 62, 72 and the proximal surface 68. Theimplant of the subject invention is fabricated from a semi-rigid orrigid material, such as a medical grade titanium. With a metal implant,a stabilizing stem would cut bone and cannot be employed to stabilizeand position the implant within the carpal row. As set forth in U.S.Pat. No.4,164,793, the disclosure of which is hereby incorporated byreference, implant 60 is provided in a variety of graduated sizes.

Stabilization of the implant in accordance with the present invention isillustrated in FIGS. 5-8. As shown in FIGS. 5 and 7, a first suture 90having ends 92, 94 is stitched to a wrist ligament. The ligament ispreferably the ulnolunate ligament 50, although others could be used.Ends 92, 94 are passed through suture passages 76, 78 and extend awayfrom scaphoid face 66 of implant 60. A second suture 96 is stitched toanother ligament, preferably the radioscapholunate ligament 48. Again,another ligament could be used. Suture 96 has ends 98, 100 which arepassed through suture passages 76, 78 so that they extend away from thetriquetrum face 64.

When the sutures have been passed through the implant body, as shown inFIG. 7, the ends 92, 94 and the ends 98, 100 may be grasped and pulledoutwardly. This pulls the lunate downwardly and into the proper positionin the proximal carpal row. As seen in FIGS. 6 and 8, the sutures arethen tied and cut to define knots 102, 104.

The implant, the sutures, the attachment to the ligaments of the wristinsure that the implant is positioned and properly stabilized. Face 64abuts against or is positioned to articulate with the triquetrum, andface 66 is positioned to articulate with the adjacent scaphoid bone.Capitate recess 70 is positioned to articulate with the head of thecapitate bone.

The present invention provides a unique implant and method forstabilizing the implant which is fabricated from rigid material. Themethod employs two simple sutures and a pair of passage formed in theimplant body. The implant and method in accordance with the presentinvention eliminates the stabilizing stem which can cause trauma to thebone. Erosion problems heretofore experienced are eliminated. Suturingthe implant to the underlying ligaments provides stability using arelatively simple surgical procedure.

In view of the foregoing description, those of ordinary skill in the artmay envision various modifications which would not depart from theinventive concepts disclosed herein. The above description should,therefore, be considered as only that of the preferred embodiment. Thetrue spirit and scope of the present invention may be determined byreference to the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as as follows:
 1. An implant forreplacement of the lunate bone, said implant comprising:a one-piece, atleast semi-rigid body, said body defining:a planar triquetrum face; aplanar scaphoid face; a cupped, concave, smooth distal surface; aproximal surface having a smooth, convex shape, said proximal surfacejoining proximal edges of said triquetrum and said scaphoid faces; adorsal surface extending between dorsal edges of said triquetrum andscaphoid faces; and a palmar surface extending between palmar lateralsurfaces of said triquetrum and scaphoid faces, said body furtherincluding a plurality of suture passages extending between and openingthrough said triquetrum and scaphoid faces.
 2. An implant as defined byclaim 1 wherein said suture passages extend in spaced, generallyparallel relationship.
 3. An implant as defined by claim 2 wherein oneof said suture passages extends adjacent said dorsal surface and one ofsaid suture passages extends adjacent said palmar surface.
 4. An implantas defined by claim 3 further including:a pair of sutures, one of saidsutures passing through said suture passages and including endsextending away from said triquetrum face and the other of said suturespassing through said suture passages and having ends extending away fromsaid scaphoid face.
 5. An implant as defined by claim 1 furtherincluding:a pair of sutures, one of said sutures passing through saidsuture passages and including ends extending away from said triquetrumface and the other of said sutures passing through said suture passagesand having ends extending away from said scaphoid face.